[Detection to changes in hyoid and tongue positions, and pharyngeal airway following mandibular setback surgery by cone beam CT].

OBJECTIVE

To observe changes in tongue and hyoid position, and pharyngeal airway in patients with skeletal class III malocclusion after the combined orthodontic and orthognathic treatment.

METHODS

Twenty patients were involved in this study. Cone beam CT (CBCT) was performed on patients one week before and six months after treatment. Raw data were reconstructed into three-dimensional model. To set up a three-dimensional reference frame, which was based by point "S", the sagittal and transversal measurements, cross sectional areas, partial and total volumes were computed. The three-dimensional position changes of chin, hyoid bone and tongue were measured in order to analyze the amount of mandibular setback relationship with the changes of pharyngeal airway, hyoid bone and tongue positions.

RESULTS

After treatment, the pharyngeal airway was constricted significantly. The hyoid significantly moved inferoposteriorly by 5.72 mm (backward) and 2.76 mm (downward) and the tongue moved posteriorly by 4.04 mm after surgery (P < 0.05). Among the 19 correlated indexes between the amount of mandibular setback and other measurements, 14 of which were significantly correlated (P < 0.05). The strongest correlation was found between the amount of mandibular setback and total volumes of pharyngeal airway (r = 0.834, P < 0.01).

CONCLUSION

Following combination therapy, the pharyngeal airway space decreased, the hyoid moved inferoposteriorly and tongue moved posteriorly. There were great correlations between the amount of mandibular setback and the changes.